Lamp base



FIG. 1 is a side view of the lamp base, with all sides being the same, the stippling representing a contrasting color;

FIG. 2 is a top view of FIG. 1; and,

FIG. 3 is a bottom view of FIG. 1.

The broken lines represent environment of use and form no part of the claim. 

The ornamental design for a lamp base, as shown and described. 